246
P.NANNELLIAND L. SACCONI
Inorganic Chemistry CONTRIBUTIOSFROM
THE
ISSTITUTE OF GENERAL ASD INORGAKIC CHEMISTRY, UXIVERSITYOF FLORENCE, FLORENCE, ITALY
Action of Hydrochloric and Hydrobromic Acids on Nickel(I1) Complexes with N- Substituted Salicylideneethylenediamines Nickel( 11) complexes of the type [SXLen-N( R)R’] 3Ni react, under suitable conditions, with hydrochloric and hydrobromic acids to form complexes of the general formula [SALen-K(R)R’]&i.2HX. When R = H the halogen ion coordinates to the central nickel atom, and paramagnetic octahedral complexes are formed with the halogen ions in LZS positions. When the ( p ) nitrogen is a tertiary nitrogen, the halogens do not bond to the nickel and diamagnetic planar complexes are obtained.
Introduction Nickel (11) complexes with Schiff bases, derived from salicylaldehydes and N-substituted ethylenediamines, have been described in previous papers.l!* The Schiff bases have the general formula CH=N-CH,-CH,-N,
/R
P
R’
‘OH
and, depending on the substituents Y, R, R’,their nickel(I1) complexes show various types of stereochemistry in the solid state with the terminal (@ nitrogen either coordinated or not coordinated to the metal atom. Planar, octahedral, and pentacoordiiiated compounds are obtained. Equilibria between the various species may occur in solution. The presence in the molecule of the amine group -N(R)R’, either free or coordinated to the central nickel atom, in compounds of this type has prompted us to examine the possibility of protonation of this group by treatment of the complex with hydrohalogen acids under suitable conditions. such a treatment is too rough, i t leads to a complete decomposition of the initial complex. However, an indirect treatment, or a direct treatment performed with great care, leads to the formation of complexes in which the nitrogen atom of the -N(R)R’ group is protonated while the anion is either coordinated to the metal atom or uncoordinated. The stereochemistry of the resulting complexes depends on the substituents R and R’ (Y = H in all cases so far examined). These compounds have been characterized and studied by magnetic measurements, optical and infrared spectra, measurements of molecular weight, and conductivity. In order to obtain conclusive information on the stereochemistry of these compounds, some analogous complexes with catechol have also been prepared and characterized. Experimental Section Preparation of Compounds.-Only typical syntheses are described. Parallel reactions were used for the preparation of related substances. [SALen-N(H)CHJ12Ni.2HBr. Method A.-[SilLen-N(H)CHH]2Ni,2.06 g. (0.005 mole), and finely ground triethylamine hydrobromide, 1.9 g . (0.0103 mole), were plawd, together irith (1) L. Sacconi, P. Sannelli, and U. Campigli,I?rovg. Chem., 4, 818 (196.5). (2) L. Sacconi, P. Nannelli, N. h-ardi, and U. Campigli, zbzd., 4 , 943 (1968).
250 ml. of dry benzene, in a 500-ml. three-necked flask equipped with a mechanical stirrer and a reflux condenser. The suspension vias stirred and refluxed for about 4 hr. After cooling the precipitate was recrystallized by dissolving it in the miuimum amount of chloroform and precipitating with ligroin. The pure product weighed 1.6 g. ( 5 5 % ) . Either Ti-methylaniline or diphenylamine hydrobromide can be used in place of triethylamine hydrobromide. Method B.-[ShLen-N(H)CH,]aNi, 1.5 g. (0.0036 mole), dissolved in ca. 500 inl. of dry benzene, was placed in a 1-1. thrccnecked flask equipped with a mechanical stirrer, a reflux condenser, and a dropping funnel with side arm. A benzene solution of hydrogen bromide, obtained by bubbling dry hydrogen bromide in the solvent for few minutes, was added dropwise to the chilled solution of the complex, with vigorous stirring, until the reaction mixture turned colorless or light green. The precipitate was then recrystallized as in method A. The yield of the pure product was 1.5 g. ( 72y0). This method was not applicable to the HC1 series. Extensive decomposition of the original complexes occurred. [SALen-N(H)CH3]zNi.CBH4(OH)2.--A mixture of 2.06 g. (0.005 mole) of [SALen-S(H)CH8]eNi and 0.6 g. (0.0054 mole) of catechol in ca. 100 ml. of benzene x a s refluxed on a steam bath for about 1 hr. After cooling the precipitate was filtered and recrystallized from an alcohol-water mixture; yield U.7 g. (2eOjG). Spectra.-Absorption spectra were recorded in the range 5000-25,000 cm.-l a t room temperature with a Beckman DR-2 spcctrophotometer and 1-cm. silica cells. Solvents were of reagent grade quality. Nitroethane was washed with 5c/;. aqueous sodium bicarbonate, dried v i t h Drierite, and fractionally distilled (b.p. 113’). Chloroform was washed six times with water, dried for 24 hr. over phosphorus pentoxide, and distilled from potassium carbonate under nitrogen. The diffuse reflcctance spectra were measured using the standard Beckman reflectance attachment and magnesium oxide as the reference. The infrared spectra were recorded on hexachlorobutadiene mulls using a Perkin-Elmer Model 337 spectrophotometer. Conductivity Measurements.-The conductivity values were measured with a WTW Model LBR/B conductance bridge. Ab. Concentrations of the solutions were approximately Molecular Weight Measurements.-Molecular weights n ere determined in chloroform a t 37;”with a Mechrolab Model 301.4 vapor pressure osmometer calibrated with benzil. Scale readings were made 2 min. after the drop of the solution was placed on the thermistor. Concentrations of the solutions were in the range 10-2-10-3 Jl. Magnetic Measurements.-The magnetic measurements were performed by the Gouy method with the apparatus and experimental technique described previously.3 The sample tube was calibrated with Hg[Co(SCS)4] and freshly distilled water.4 ca.
(H) L. Sacconi, K. Cini, h l . Ciainpulini, and I’. X a g g i u , J . A m . C I i ? i n . .Yoc., 8 2 , 3487 (1960).
(4) B. N. Figgis and I-. Lewis, “Modern Coordination Chemistry,” J. Lewis and L. Wilkins, Ed., Interscience Publishers, Inc., New Yoi-k, S . Y . . 1960, p. 415.
AND HYDROBROMIC ACIDSON NICKEL(II)COMPLEXES247 VoZ. 5, No. 2, February 1966 ACTIONOF HYDROCHLORIC
TABLE I
SUMMARY OF PHYSICAL AND ANALYTICAL DATAFOR SUBSTITUTED [SALen-N( R)Rf]zNi.2HX A N D [SALen-N( R)RfIzNiG,H4(OH)z COMPLEXES -N (R) R‘
M.p., ‘C.
Crystallization
Acid
IIa
+ ligroin CHC13 + petr. ether
I11
CzH60H
IV”
CHC13
V
CHCls
VI
CzHpOH
VI1
CHIOH f ether
225
+ ether
237-239
CHCla
I
>340 264
+ HzO
-Analysis, %*-H N
C
183-184
142-144 152 187-189
Ni
49.41 49.10 41.77 42.30 59.67 59.95
5.80 5.71 4.90 5.20 6.16 6.36
11.52 11.67 9.74 9.71 10.70 10.91
12.07 12.34 10.20 9.78 11.21 11.51
59.04 58.60 51.53 51.60 66.78 66.97
5.28 5.35 4.61 4.85 5.60 5.87
9.18 8.91 8.01 7.93 8.65 8.77
9.61 9.21 8.39 8.18 9.06 9.21
47.37 47.50
6.11 6.10
8.50 8.78
8.90 9.14
49.22 8.20 8.59 5.90 49.17 6.15 8.21 8.49 a Compounds I1 and IV show molar conductance values of 3 and 10 cm.Z/ohm M , respectively. The conductivity measurements were made on 1 x 10-3 M solutions in nitraethane. Typical molar conductances for 1: 1 and 1: 2 electrolytes in 10-3 M solutions are in the ] I and [(CH,)JX]Z[CO(NCS)~] First = 160. ranges 70-85 and 145-160 cm.Z/ohm M , respectively. For example [ ( ~ - C ~ H S ) ~=N 83 line for each substance is the calculated value; the second is the found. CHaOH
VI11
TABLE I1 MAGNETIC SUSCEPTIBILITY DATAFOR SUBSTITUTED [SALen-N(R)Rf]2Ni.2HX AND [SALen-NfR)R’]zNi.C6H4(OH)z COMPLEXES IN THE SOLID STATE Temp.,
OC.
Compound
lop0
W a v e l e n g t h , my , 8vO O 6:
,
5yO
Serf.
1OSXs
lOeXN,a
B.M.
I 19 7.84 4100 3.11 I1 19 6.49 4045 3.10 I11 19 7.40 4170 3.14 IV 16 5.74 3875 3.00 V 27 4.83 3860 3.06 VI 20 5.25 3770 2.98 VI1 19 b VI11 17 b Corrected for diamagnetic contribution as calculated from Pascal’s constants (P. W. Selwood, “Magnetochemistry,” 2nd Ed., Interscience Publishers, Inc., New York, N. Y . , 1956). Diamagnetic.
Results Series I : -N(R)R’ = -N(H)CH3, -N(H)CeHS.-The treatment with either HCI or HBr, free or as salts of aliphatic or aromatic amines, leads in every case to bright gray-green compounds which are soluble in alcohol, sparingly soluble in chloroform, and insoluble in nonpolar solvents. When R’ = CHz the complexes are soluble in water. The analytical data (Table I) suggest the general formula [SALen-N(R)R’]sNi.2HX for these reaction products. All the compounds of this series are paramagnetic with values of heft = 3.1 B.M. (Table 11). Measurements of conductivity in nitroethane, for the compounds sufficiently soluble in this solvent, give molar conductance values 10 cm.2/ohm M (Table I), compared with values of ca. 80 and 150 u “ / o h m M for uni-univalent and uni-bivalent electrolytes under the same conditions. This indicates that the halogen is bonded to the metal
NH2+ group, associated via a weak hydrogen bond. In the halogen salts of the amines such a frequency can be found in the region 2400-2900 cm.-l and shows a remarkably fine structure, as i t presents itself a t times as a quadruplet. The frequency of these bands does not differ with various halogens, although the relative intensities vary.j The absorption frequencies due to the stretching of the free N H f group, secondary or tertiary, are located a t ca. 3200 cm. -I, as has been seen in the spectra of amine salts with large anions of the type c104-, PFs-, etc. These bands do not show a fine structure, as is to be expected because hydrogen bonds are absent.6 In our compounds we observe a quadruplet between 3000 and 3500 cm.-l with various relative intensities depending on the halogen and with the highest intensity a t ca. 3200 cm.-l. This appears to represent an intermediate situation between the two extremes quoted above. In order to obtain further information on the stereochemistry of these complexes, me have also examined the products of the reaction between the same initial complexes and catechol. Bright green compounds are formed for R’ = C6H5 and ochre for R’ = CHx. The analytical data of these derivatives indicate a formula of the type ISALen-N(H)R’l2NiC6H4(0H)2(Table I). These compounds are also paramagnetic (Table 11) and their electronic spectra are substantially the same as those of the analogous halogen complexes, in the solid state as well as in solutions of chloroform and nitroethane (Figure 1 and Table 111). (5) R. C. Lord a n d R. E. Merrifield, J . C h e w . P h y s . , 21, 1 G G (1953). (6) R. H. iTutta1, D. W. A . Sharp, and T. C. Waddington, J . Chem. Soc., 4966 (1960).
4000
3000
Frequency, cm
-’
2000
Figure 2.-Infrared spectra of [SALen-K(H)CH3]QXi. 2HCl (curve A ) ; [SALen-S(H)CH3]2Ni.2HBr (curve B); [SALenN(H)CeHj]2h7i.2HC1 (curve C ) ; [SALen-N(H)C6HSI2Ni.2HBr (curve D ) : [SALen-N( C2Hj)2]2Ni.2HBr (curve E); [SALenN(CH2)6]2Ni.2HBr (curve F).
Series I1 : -N(R)R’ = -N(C2H&, -N(CH2)5.-A1though i t has so far not been possible to isolate or identify the products resulting from the treatment with HC1, action of HBr gives products with a more intense green color which are insoluble in chloroform, nitroethane, and nonpolar solvents, but soluble in both alcohol and water. The analytical data (Table I) are in accordance with a formula of the type [SALenN(R)R’]*Ni*2HBr. These compounds are, however, diamagnetic and the reflectance spectra do not show absorption bands below 14,000 cm.-l (Figure 1). Infrared spectra, in hexachlorobutadiene mull, show absorption bands in the region 2400-2800 cni.-l (Figure 2), i.e., in the region where the + N H + stretching fre-
vel. 6 , A70. 2, February 1966 ACTION ON HYDKOCHLOKIC AND HYDKOBWMIC ACIDSON NICKEL(II)COMPLEXES249
quencies are found for normal hydrobromides of tertiary amines.’ Because these reaction products are insoluble in (‘inert’’solvents i t has not been possible to study their behavior in solution. Discussion In Ni(I1) complexes with Schiff bases derived from salicylaldehydes and N-substituted ethylenediamines, the ligand molecule is bi- or tridentate, according to the substituents Y, R, R’. In general, for a given Y, octahedral forms are favored in the case of both electron-releasing and small R, R’ groups, while planar forms are obtained in the case of large and electronattracting substituents. In intermediate cases pentacoordinated complexes are also obtained.2 Different structures, depending on the variations of R and R’, can be assigned to the halogen derivatives of this class of compounds. While conductivity measurement data suggest, for the compounds of series I, that the halogens are coordinated to the central nickel atom, the magnetic and spectral data lead us to assign a distorted octahedral configuration to them. The spectra are in fact those of a distorted octahedral structure. The bands a t 8500 and 10,000-11,500 cm.-l can be assigned to the components of the V I transition (3Az,(F) --+ 3T2g(F)) in a regular octahedral field, which is split due to the distortion of the environment, while the third band can be attributed to the ~2 transition (3A2g(F)4 3T1g(F)).The magnetic and spectral data do not, however, yield any information regarding the two possible structures, cis and trans, for the halogen atoms. Nevertheless, a comparison of the spectra of these com-
L/ I1
I
111 pounds and those derived from catechol shows that the two types of spectra are substantially the same (Figure 1). Because the derivatives of catechol must of neces(7) B. Chenon and C. Sandorfy, Can. J. Chem., 36, 1181 (1958)
sity be cis forms (11), the cis configuration (I) must be assigned to the complexes of series I. The diamagnetism and the absence of absorption below 14,000 cm.-l in the crystal field spectra of the derivatives of series I1 leads us to attribute a trans planar structure of type I11 to them. In this structure the bromide ions are not coordinated to the central nickel. The occurrence of planar and octahedral structures, for the states described here, cannot be easily explained only on the basis of steric effects of the R and R’substituents or of different dqnor properties of the (P) nitrogen with various R and R’ groups. This donor grouping is, in each case, outside the coordination sphere because of the protonation of the nitrogen. On the other hand i t is noticeable that a distorted octahedral structure is obtained when the terminal amine group is a secondary -N(H)R’ group. Planar complexes are, however, obtained when this amine group is tertiary, of the -N(R)R’ type. It is known that in amine salts with hydrohalogen acids, hydrogen bonds of the type +NH+...X- are stronger in the case of tertiary amines than in secondary ones. This difference may explain the two different stereochemical forms observed in our complexes. When the nitrogen is secondary (series I ) , it is attached to the halogen atom by relatively weak bonds, thus allowing the halogen to coordinate to the metal atom. It may be observed from the infrared spectra that the hydrogen bonds >NHzf...X- are rather weak in this case. The molecular weight measurements in chloroform solution suggest the existence of weak intermolecular hydrogen bonds in this solvent, but i t cannot be excluded that the rather high molecular weight values are the result of molecular associations of the dipole-dipole type. In the compounds of series I1 a tertiary (P) nitrogen is present, and the polarization of the halogen, due to strong hydrogen bonding with the protonated amine group, prevents the coordination of the halogen ion to the central nickel. This interpretation is confirmed by the infrared spectra of these compounds, which show absorptions characteristic of normal salts of tertiary amines. Acknowledgment.-Thanks are expressed to Dr. J. Gelsomini for microanalysis and to Dr. M. Marzocchi for helpful discussions on infrared spectra. The financial support of the Italian “Consiglio Nazionale delle Ricerche” and of the Scientific Affairs Division of NATO is gratefully acknowledged.
